Best option is to get a Z2 "backbone" and tray, and remove the rest of the feedneck fragments on your neck and use them along with your other prophecy components on the new Z2 backbone with integrated feedneck.

Yup. Just did that this weekend. Works great. My shell hasn't broken and has lasted me a while, but I wanted a neck that can fit in older clamping feednecks that have small tolerances out of the factory. The z2 feedneck is slightly smaller than the shell/feedneck combination on the original prophecy and also has some flexibility when squeezing it into a marker.

You also will just need the backbone unless you plan to use a z2 shell in the future. The existing floor will work because you will be using original prophecy shells, and the tab on that floor is designed for it. I bought the z2 floor thinking I would need it, but it leaves a weird space between the shell and slide when installed.